Cumene (isopropylbenzene) is a key raw material in the production of phenol and acetone and is produced primarily by the propylation reaction of propylene, C3H6, and benzene, C6H6, in a catalytic environment. Cumene is then converted to phenol and acetone by peroxidation. When sold as a commodity product, the product will usually contain at least 99.70 weight percent of cumene based on the weight of the product.
A source of benzene is reformate, which is prepared by contacting a mixture of petroleum naphtha and hydrogen with a reforming catalyst containing a support, e.g., halogen-treated alumina or non-acidic zeolite L, and a hydrogenation/dehydrogenation metal, e.g., Group 8, 9, or 10 metal such as platinum. That process typically produces a reformate that includes C5-hydrocarbons, C6-C8 aromatic hydrocarbons, e.g., benzene, C9+ hydrocarbons, C6+ paraffins, and cycloparaffins (naphthenes).
Another source of benzene is the cracking of hydrocarbons such as by steam cracking or catalytic cracking. That process typically produces an effluent that includes C6-C8 aromatic hydrocarbons, e.g., benzene, C6+ paraffins, and naphthenes.
Still another source for producing aromatics is the dehydrocyclo-oligomerization of C2-C5 aliphatic hydrocarbons. That process typically produces a product effluent that includes C6-C8 aromatic hydrocarbons, e.g., benzene, C6+ paraffins, naphthenes and C5 aliphatic hydrocarbons.
Benzene can be separated from other reformate hydrocarbons, e.g., C7+ aromatics, by distillation. However, the benzene obtained by distillation will usually contain C6 and C7 non-aromatic hydrocarbon impurities that are difficult to separate from benzene by distillation because they have boiling points close to the boiling point of benzene, i.e., their boiling point is within 10° C. of benzene (boiling point of 80.1° C.) at a pressure of about 101.3 kPa-a (absolute). This feed may also contain C5 paraffins and naphthenes, such as n-pentane and cyclopentane. These impurities, which are hereinafter sometimes referred to as “benzene coboilers”, may be present in the distillate product in an amount up to 75 percent by weight based on the weight of the product. Examples of benzene coboilers include cyclohexane, methylcyclopentane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 2,4-dimethylpentane, and dimethylcyclopentane.
Because of the presence of benzene coboilers, the feed usually undergoes an additional step, i.e., extraction such as liquid extraction or extractive distillation, to remove benzene coboilers from the benzene product before the benzene is propylated to form cumene. Generally, benzene used in the propylation of benzene to produce high purity cumene has a purity of about at least 99.985 weight percent by weight based on the weight of benzene present in the benzene distillate. However, the extraction step is expensive and time consuming, which results in increased costs in manufacture of high purity cumene. It would be highly advantageous to use lower cost refinery streams rich in benzene, for example, aromatizer product streams which have not undergone extraction to produce high purity cumene.
In addition, processes for producing cumene by the propylation of benzene usually result in the formation of polypropylbenzenes which are processed by transalkylation with benzene to form cumene. A problem associated with the transalkylation of polypropylbenzenes is that several impurities, e.g., ethylbenzene, are usually formed as by-products. Formation of by-product ethylbenzene is industrially disadvantageous because its boiling point is relatively close to that of cumene. As a result, the separation of ethylbenzene from cumene to obtain high purity cumene requires the use of a special distillation column which results in increased costs in manufacture of high purity cumene.
By the present disclosure, a process is provided for the propylation of benzene to produce high purity cumene that uses a hydrocarbon composition feed containing benzene that has not undergone extraction. In addition, the process of the present disclosure does not require the transalkylation of the polypropylbenzenes formed during the propylation of benzene.